Water distillation in the extraction of essential oils.
In the manufacture of essential oils using the method of water distillation, the botanic material is completely immersed in water and the still is brought to the boil. This method protects the oils so extracted to a certain degree since the surrounding water acts as a barrier to prevent it from overheating. When the condensed material cools down, the water and essential oil is separated and the oil decanted to be used as essential oil. The water that is so separated in this process is also used and is marketed as "floral waters" (also called hydrosol or sweet water) - such as rosewater, lavender water and orange water. Water distillation can be done at reduced pressure (under vacuum) to reduce the temperature to less than 100 degrees, which is beneficial in protecting the botanical material, as well as the essential oils.
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Steam Distillation
Steam distillation is the most common method of extracting essential oils. Steam distillation is done in a still. Fresh, or sometimes dried, botanical material is placed in the plant chamber of the still, and pressurized steam is generated in a separate chamber and circulated through the plant material. The heat of the steam forces the tiny intercellular pockets that hold the essential oils to open and release them. The temperature of the steam must be high enough to open the pouches, yet not so high that it destroys the plants or fractures or burns the essential oils. As they are released, the tiny droplets of essential oil evaporate and, together with the steam molecules, travel through a tube into the still's condensation chamber. As the steam cools,it condenses into water. The essential oil forms a film on the surface of the water. To separate the essential oil from the water, the film is then decanted or skimmed off the top. The remaining water, a byproduct of distillation, is called floral water, distillate, or hydrosol. It retains many of the therapeutic properties of the plant, making it valuable in skin care for facial mists and toners.
Cold Pressing
Another method of extracting essential oils is coldpressed expression, or scarification. It is used to obtain citrus fruit oils. In this process, fruit rolls over a trough with sharp projections that penetrate the peel. This pierces the tiny pouches containing the essential oil. Then the whole fruit is pressed to squeeze the juice from the pulp and to release the essential oil from the pouches. The essential oil rises to the surface of the juice and is separated from the juice by centrifugation.
Enfleurage
Some flowers, such as jasmine or tuberose, have such low contents of essential oil or are so delicate that heating them would destroy the blossoms before releasing the essential oils. In such cases, an expensive and lengthy process called enfleurage is sometimes used to remove the essential oils. Flower petals are placed on trays of odorless vegetable or animal fat, which will absorb the flowers' essential oils. Every day or every few hours, after the vegetable or fat has absorbed as much of the essential oil as possible, the depleted petals are removed and replaced with fresh ones. This procedure continues until the fat or oil becomes saturated with the essential oil. Adding alcohol to this enfleurage mixture separates the essential oil from the fatty substance. Afterwards, the alcohol evaporates and only the essential oil remains.
Solvent Extraction
Another method of extraction used on delicate plants is solvent extraction, which yields a higher amount of essential oil at a lower cost. In this process, a chemical solvent such as hexane is used to saturate the plant material and pull out the aromatic compounds. This renders a substance called a concrete. The concrete can then be dissolved in alcohol to remove the solvent. When the alcohol evaporates, an absolute remains. Some trees, such as benzoin, frankincense, and myrrh, exude aromatic 'tears', or sap that is too thick to use easily in aromatherapy. In these cases, a resin or essential oil can be extracted from the tears with alcohol or a solvent such as hexane. This renders a resin or an essential oil that is easier to use.
Turbodistillation, Hydrodiffusion, and Carbon Dioxide Extraction
Turbodistillation is suitable for hard-to-extract or coarse plant material, such as bark, roots, and seeds. In this process, the plants soak in water and steam is circulated through this plant and water mixture. Throughout the entire process, the same water is continually recycled through the plant material. This method allows faster extraction of essential oils from hard-to-extract plant materials.
In the hydrodiffusion process, steam at atmospheric pressure is dispersed through the plant material from the top of the plant chamber. In this way the steam can saturate the plants more evenly and in less time than with steam distillation.
Supercritical carbon dioxide extraction uses carbon dioxide under extremely high pressure to extract essential oils. Plants are placed in a stainless steel tank and, as carbon dioxide is injected into the tank, pressure inside the tank builds. Under high pressure, the carbon dioxide turns into a liquid and acts as a solvent to extract the essential oils from the plants. When the pressure is decreased, the carbon dioxide returns to a gaseous state.
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